2). I really don't understand why we should use Twig : Smarty is older, why using yet another template engine ? Or I've got a better idea : we could use the template engine used in phpBB2 : he's older !

I'm agree that standardization would be just fine(c), and I like the Twig syntax, but I think the "YATL, we should use Twig" argument is not relevant.